Conventional methods of high resolution optical microscopy and the new Allen Video Enhanced Contrast polarized light (AVEC-POL) and differential interference contrast (AVEC-DIC) techniques will be used to explore motility, spreading and the release reaction in living platelets from normal individuals and patients with clotting and bleeding disorders. Some experiments will be carried out on the effects of drugs on platelet motility and release. The development of the cytoskeletal structure of spreading platelets will be examined by a combination of electron microscopical techniques and immunofluorescence microscopy.